Recent Advances on Metal Oxide Based Sensors for Environmental Gas Pollutants Detection.

Optimizing materials and associated structures for detecting various environmental gas pollutant concentrations has been a major challenge in environmental sensing technology. Semiconducting metal oxides (SMOs) fabricated at the nanoscale are a class of sensor technology in which metallic species are functionalized with various dopants to modify their chemiresistivity and crystalline scaffolding properties. Studies focused on recent advances of gas sensors utilizing metal oxide nanostructures with a special emphasis on the structure-surface property relationships of some typical n-type and p-type SMOs for efficient gas detection are presented. Strategies to enhance the gas sensor performances are also discussed. These oxide material sensors have several advantages such as ease of handling, portability, and doped-based SMO sensing detection ability of environmental gas pollutants at low temperatures. SMO sensors have displayed excellent sensitivity, selectivity, and robustness. In addition, the hybrid SMO sensors showed exceptional selectivity to some CWAs when irradiated with visible light while also displaying high reversibility and humidity independence. Results showed that TiO2 surfaces can sense 50 ppm SO2 in the presence of UV light and under operating temperatures of 298-473 K. Hybrid SMO displayed excellent gas sensing response. For example, a CuO-ZnO nanoparticle network of a 4:1 vol.% CuO/ZnO ratio exhibited responses three times greater than pure CuO sensors and six times greater than pure ZnO sensors toward H2S. This review provides a critical discussion of modified gas pollutant sensing capabilities of metal oxide nanoparticles under ambient conditions, focusing on reported results during the past two decades on gas pollutants sensing.

Applicability of Titanium-Based Catalysts in the Photocatalytic Degradation of 2,3,7,8-Tetrachlorodibenzofuran.

Polychlorinated dibenzofurans (PCDFs) are persistent toxic compounds that are ubiquitous in the environment. Nanocomposites of titanium(IV) oxide-vanadium(III) oxide (Ti3V2O7) and titanium(IV) oxide-silicon dioxide (Ti2Si7O30) were prepared and spectroscopically analyzed as potential decontaminants for dioxin-like materials. The analysis confirmed a homogeneous morphology with nanoscale particle size. The Ti-Si sample was found to have a high surface area compared to the Ti-V composite. Vanadium(III) oxide (V2O5) and silicon dioxide (SiO2) were chosen as materials for the formation of heterogeneous compounds with titanium(IV) oxide (TiO2) because they possess a suitable band alignment with TiO2, thus forming effective photocatalysts. This study evaluated the photodegradation of 2,3,7,8-tetrachlorodibenzo-furan (TCDF) in the presence of Ti-Si and Ti-V oxide composites, which was tested using high- (254 nm) and midenergy (302 nm) UV irradiation sources. While Ti-Si showed success in the photodegradation of 2,3,7,8-TCDF dissolved in a (1:1) methanol-tetrahydrofuran (MeOH-THF) solution, the Ti-V composite proved to be a powerful material in adsorbing TCDF with a high capacity immediately upon mixing. Ti-Si oxide was found to decompose TCDF under the two irradiation sources with 98-99% degradation occurring after 70 min. The use of 254 nm as an irradiation source in the presence of Ti-Si was 4.3 times faster than the analogue reaction irradiated without a catalyst. Byproducts of the degradation were evaluated using gas chromatography-mass spectrometry (GC-MS), resulting in a lower chlorinated congener and less toxicity, as the main degradation product.

Junk food: Polymer composition of macroplastic marine debris ingested by green and loggerhead sea turtles from the Gulf of Oman.

Pollution of the marine environment by plastic marine debris has become one of the most pervasive threats impacting marine environments. In this study, for the first time, we evaluate the polymer types of the plastic marine debris ingested by 49 green and 14 loggerhead sea turtle strandings in the Gulf of Oman. Plastic marine debris was ingested by 73.5% of green and 42.9% of loggerhead sea turtles in this study. Overall, evidence suggested that green sea turtles from the Gulf of Oman coast of the United Arab Emirates ingested high levels of plastic marine debris, predominantly Polypropylene (PP) & Polyethylene (PE), followed by Nylon, PP-PE mixture, Polystyrene (PS), Poly vinyl chloride (PVC) and Ethylene vinyl acetate (EVA), respectively. Loggerhead sea turtles also ingested high levels of plastic marine debris, which also predominantly consisted of PP & PE, followed by PP-PE mixture, Nylon and PS. While recent studies were directed into polymer characterization of micro-plastics in aquatic life, our study focuses on macro-plastics which impose significantly greater risks.

Phytochemical profile and antiproliferative activities of acetone extracts of Asplenium polypodioides Blume. and A. dalhousiae Hook. in MDA-MB-231 breast cancer cells.

The plants extracts are widely used in traditional medicines and hence considered a potential source for drug discovery. In this study, we assessed the phytochemical composition of Asplenium dalhousiae and Asplenium polypodioides in acetone extracts and checked its antiproliferative potential in MDA-MB-231 cells. We found that both plants are rich in phenolic and flavonoid compounds and are efficient in antioxidant activities. The total phenolic compounds in A. dalhousiae were 44.15 ± 1.38 µg/mg whereas in A. polypodioides were 27.73 ± 1.35 µg/mg. Total flavonoids in A. dalhousiae were 105.39 ± 2.92 µg/mg whereas in A. polypodioides were 101.56 ± 1.75 µg/mg. The ferric reducing power assay indicates 66.38 ± 2.6% reduction by A. dalhousiae whereas 78.43 ± 0.47% reduction by A. polypodioides. Similarly, the total antioxidant capacity of A. dalhousiae was found to be 59.95 ± 1.13 whereas for A. polypodioides the recorded value was 33.03 ± 1.67%. Using GCMS analysis, we identified 25 compounds in A. dalhousiae whereas 26 in A. polypodioides. Four of these compounds are common in both plants. The morphological study and MTT assay revealed that both plants have antiproliferative potential as both plants exerted significant effects on the shape of the MDA-MB-231 cells and inhibited cellular proliferation in time and dose dependent manner. We conclude that both Asplenium plants have potential anticancer compounds.

Lysozyme and Human Serum Albumin Proteins as Potential Nitric Oxide Cardiovascular Drug Carriers: Theoretical and Experimental Investigation.

Nitric oxide-containing drugs present a critical remedy for cardiovascular diseases. Nitroglycerin (NG, O-NO) and S-nitrosoglutathione (SNG, S-NO) are the most common nitric oxide drugs for cardiovascular diseases. Insights regarding the binding affinity of NO drugs with lysozyme and human serum albumin (HSA) proteins and their dissociation mechanism will provide inquisitive information regarding the potential of the proteins as drug carriers. For the first time, the binding interactions and affinities are investigated using molecular docking, conventional molecular dynamics, steered molecular dynamics, and umbrella sampling to explore the ability of both proteins to act as nitric oxide drug carriers. The molecular dynamics simulation results showed higher stability of lysozyme-drug complexes compared to HSA. For lysozyme, cardiovascular drugs were bound in the protein cavity mainly by the electrostatic and hydrogen bond interactions with residues ASP53, GLN58, ILE59, ARG62, TRP64, ASP102, and TRP109. For HSA, key binding residues were ARG410, TYR411, LYS414, ARG485, GLU450, ARG486, and SER489. The free energy profiles produced from umbrella sampling also suggest that lysozyme-drug complexes had better binding affinity than HSA-drug. Binding characteristics of nitric oxide-containing drugs NG and SNG to lysozyme and HSA proteins were studied using fluorescence and UV-vis absorption spectroscopy. The relative change in the fluorescence intensity as a function of drug concentrations was analyzed using Stern-Volmer calculations. This was also confirmed by the change in the UV-vis spectra. Fluorescence quenching results of both proteins with the drugs, based on the binding constant values, demonstrated significantly weak binding affinity to NG and strong binding affinity to SNG. Both computational and experimental studies provided important data for understanding protein-drug interactions and will aid in developing potential drug carrier systems in cardiovascular diseases.

FRET-based fluorescent probe for drug assay from amino acid@gold-carbon nanoparticles.

Biocompatible and luminescent nanostructures synthesized by capping gold-carbon nanoparticles (HOOC-4-C6H4-AuNPs) with amino acids tyrosine, tryptophan, and cysteine were used for the quantitative estimation of ranitidine (RNH), a peptic ulcer and gastroesophageal reflux drug. We applied a fluorescence quenching mechanism to investigate the viability of the energy transfer based on gold-carbon nanosensors. Förster resonance energy transfer (FRET) calculations showed a donor-acceptor distance of 1.69 nm (Tyr@AuNPs), 2.27 nm (Trp@AuNPs), and 2.32 nm (Cys@AuNPs). The constant time-resolved fluorescence lifetime measurements supported the static quenching nature. This method was successfully utilized in the detection and quantification of RNH, with a limit of detection (LOD) of 0.174, 0.56, and 0.332 µM for Tyr@AuNP, Trp@AuNP, and Cys@AuNP bioconjugates, respectively. This approach was also successful in the quantification of RNH in spiked serum samples.

Meteorological patterns, technical validation, and chemical comparison of atmospheric dust depositions and bulk sand in the Arabian Gulf region.

This study reports seasonal variations of meteorological parameters, atmospheric dust and dust-borne heavy metals concentrations measured, over a period of two years, next to two major airports (Dubai International Airport and Abu Dhabi International Airport) in the Gulf Cooperation Council (GCC) region. On-line monitoring stations were installed at each location next to dust samplers used to frequently collect PM2.5 and PM10 on Teflon filters for metal analysis. Clear seasonal variation in meteorological parameters were identified. The particulate matter concentrations depicted from the two locations were continuously monitored. The PM2.5 concentration ranged from 50 to 100 µg/m3 on normal days but reached 350-400 µg/m3 per day during mild storms. The PM10 levels ranged between 100 and 250 µg/m3 during normal days and spiked to 750 µg/m3 during mild storms. Energy Dispersive X-Ray Analysis (EDS) revealed the presence of significant amounts of alkali and alkaline earth metals, which pose potential harm to aircraft engines. ICP analysis showed the presence of heavy and toxic metals in concentrations that may pose harm to human health. Bulk sand samples from Abu Dhabi sites showed chemical similarities to the atmospheric dust samples. The concentrations of heavy metals, PM2.5, and PM10 are at levels that require further monitoring due to their impact on human health. The two years meteorological monitoring, with the seasonal variations, provided additional regional data in the Arabian Gulf. Furthermore, the study concluded that Sand and Dust storms (SDS) occur more frequently at the northern Arabian Gulf compared to its southern region. The chemical correlation between atmospheric dust and regional desert sand suggests the localized origin of the smaller dust particles that may form by breaking apart of the ground sand grains. As a result of the ongoing urbanization in the region, it is essential to collect additional data from various locations for a longer period of time.

Investigating the Fluorescence Quenching of Doxorubicin in Folic Acid Solutions and its Relation to Ligand-Targeted Nanocarriers.

Folic acid (FA) is one of the most utilized moieties in active (ligand) drug delivery. The folate receptor is widely expressed on the surface of several cell lines and tumors; including ovarian, brain, kidney, breast, and lung cancers. During our previous experiments with Doxorubicin (Dox) encapsulated in folate-targeted micelles, we found that flow cytometry underestimated the amount of drug that accu- mulates inside cells. We attributed this effect to the quenching of Dox by FA and herein investigate this phenomenon in an attempt to obtain a correction factor that could be applied to the fluorescence of Dox in the presence of FA. Initially, we examine the effect of pH on the fluorescence spectra of FA, Dox, equimolar solutions of FA and Dox in water, HCI (0.1 M), and NaOH (0.1 M) solutions. We then measure the effect of the gradual increase of FA concentration on the fluorescence intensity of Dox in phosphate-buffered saline (PBS) solutions (pH of 7.4). Using the Stern-Volmer equation, we estimate the association constant of FA-Dox to be K(SV) = 1.5 x 10(4) M(-1). Such an association constant indicates that at the concentrations of FA used in targeted drug delivery systems, a significant concentration of Dox exists as FA-Dox complexes with a quenched fluorescence. Therefore, we conclude that when Dox is used in FA-active drug delivery systems, a correction factor is needed to predict the correct fluorescence intensity of agent in vitro and in vivo.

Photocatalysis of fenoxycarb over silver-modified zeolites.

Two samples of silver doped into zeolite Y were prepared and characterized. ICP and SEM-EDS analysis indicate that the AgY1 sample contains twice the amount of silver compared to the AgY2 sample. Solid state luminescence spectroscopy shows variations in the emission modes of the site-selective luminescence where various luminophores might be excited upon selecting the proper excitation energy. The selected material effectively decomposed the pesticide fenoxycarb in aqueous solution. The photodecomposition of fenoxycarb reached 80 % upon irradiation for 60 min in the presence of the AgY1 catalyst. 2-(4-Phenoxy-phenoxy)ethyl] carbamic acid (1) and 1-amine-2-(phenoxy-4-ol) ethane (2) were identified as products for both uncatalyzed solution and the catalyzed fenoxycarb with AgY2 catalyst. Whereas, compound (2) was the only product identified in the catalyzed reaction with AgY1.

Recent advances in gold and silver nanoparticles: synthesis and applications.

In the last decade, gold and silver nanomaterials have received considerable attention due to their attractive electronic and chemical properties and their potential applications in the development of new technologies. Recent advances in the study of various gold and silver nanomaterials have led to their utilization in a number of very important applications including biosensing, diagnostic imaging, and cancer diagnosis and therapy. This review surveys the various synthetic methods of gold and silver nanomaterials. Recent experimental studies focusing on the use of gold and silver nanomaterials in catalysis, food industry, and environmental conservation are also reviewed. This review also highlights the advantages of gold and silver nanomaterials in the development of fluorescence biosensors, glucose biosensors, nucleic acids-based biosensors, and protein-based biosensors. Moreover, the potent in vitro and in vivo anti-microbial and cyto-genotoxic effects of various gold and silver nanomaterials are underlined. Finally, recent advances in the employment of gold and silver nanomaterials as effective drug delivery vehicles and promising cancer therapeutic agents are summarized. Despite their use in remediating numerous medical and health-related conditions, the efficacy and safety of many gold and silver nanomaterials is still under some scrutiny. Needless to say, researchers are facing many challenges and obstacles in their ample attempts to synthesize nanomaterials that are relatively easy to design, inexpensive to fabricate, and effective in treating various diseases, but at the same time display a very low, if any, toxicity to the body. Future investigations should aim at overcoming such challenges in an attempt to design nanomaterials that will prove to be useful in diagnosing and treating life-threatening diseases while ensuring a high degree of efficacy and safety.

Carbon nanotube-ionic liquid composite sensors and biosensors.

A new composite electrode has been fabricated using multiwall carbon nanotubes (MWCNT) and the ionic liquid n-octylpyridinum hexafluorophosphate (OPFP). This electrode shows very attractive electrochemical performances compared to other conventional electrodes using graphite and mineral oil, notably improved sensitivity and stability. One major advantage of this electrode compared to other electrodes using carbon nanotubes and other ionic liquids is its extremely low capacitance and background currents. A 10% (w/w) loading of MWCNT was selected as the optimal composition based on voltammetric results, as well as the stability of the background response in solution. The new composite electrode showed good activity toward hydrogen peroxide and NADH, with the possibility of fabricating a sensitive biosensor for glucose and alcohol using glucose oxidase and alcohol dehydrogenase, respectively, by simply incorporating the specific enzyme within the composite matrix. The marked electrode stability and antifouling features toward NADH oxidation was much higher for this composite compared to a bare glassy carbon electrode. While a loading of 2% MWCNT showed very poor electrochemical behavior, a large enhancement was observed upon gentle heating to 70 degrees C, which gave a response similar to the optimum composition of 10%. The ease of preparation, low background current, high sensitivity, stability, and small loading of nanotubes using this composite can create new novel avenues and applications for fabricating robust sensors and biosensors for many important species.

Semiconducting metal oxide based sensors for selective gas pollutant detection.

A review of some papers published in the last fifty years that focus on the semiconducting metal oxide (SMO) based sensors for the selective and sensitive detection of various environmental pollutants is presented.

Dual WO(3) based sensors to selectively detect DMMP in the presence of alcohols.

A size selective approach to improving selectivity in semiconducting metal oxides (SMO) sensors was obtained by tailoring the architecture of WO(3) powders. The key for achieving high selectivity is based on using a dual sensor configuration where the response on a porous WO(3) powder sensor was compared to the response on a nonporous WO(3) powder sensor. Detection selectivity between methanol and dimethyl methylphosphonate (DMMP) is obtained because the access of a gas molecule in the interior pore structure of WO(3) is size dependent leading to a size dependant magnitude change in the conductivity of SMO sensor.

Photodecomposition of carbaryl in the presence of silver-doped zeolite Y and Suwannee River natural organic matter.

The synthesis and characterization of a novel catalyst for the photodecomposition of carbaryl (1-naphthyl, N-methylcarbamate) is reported. In the absence of a catalyst, but in the presence of UV light a 30 ppm solution of carbaryl decomposes with a first-order rate constant of (5.6 +/- 0.3) x 10(-5) s(-1) (298 K) and a quantum efficiency of 4.8 x 10(-3) molecules/photon. In the presence of the Ag-zeolite Y catalyst with 2.42% Ag by weight, the photodecomposition rate becomes 80 times faster. The addition of Suwannee River natural organic matter (NOM), which can inactivate photocatalysts, has a minimal effect on this system. In the presence of three different concentrations of NOM and 30 ppm carbaryl, our results indicate that the NOM increases or decreases the catalytic photodecomposition rate by only a factor of 3 at most.